In recent years, electric motors mounted in electrical apparatuses, such as ventilation apparatuses, are required to have preferable controllability, in addition to inexpensiveness, higher efficiencies and quietness. In this case, electric motors having preferable controllability refer to those which are capable of ventilation with optimum air quantities, depending on the conditions of rooms, without being influenced by pressure losses caused by duct pipe shapes and by pressure-loss changes caused by external wind pressures or clogging in filters and the like. PTL 1 discloses the structure of a conventional electric motor of this type.
Hereinafter, with reference to FIG. 11, a conventional electric motor will be described. FIG. 11 is a block diagram illustrating the conventional electric motor. As illustrated in FIG. 11, electric motor 101 includes driving logic control portion 105 and inverter circuit 106. Further, electric motor 101 includes designated current value change portion 117, current value designation portion 119, and supply current value control portion 122. In this case, designated current value change portion 117 controls characteristics of the current with respect to the output voltage from lower-DC-voltage conversion portion 108, which is adapted to supply a power supply to inverter circuit 106, such that the current linearly increases with increasing output voltage.
This conventional electric motor 101 has had the problem that it has not been able to make differences between amounts of air blowing at lower humidity and amounts of air blowing at higher humidity, depending on the humidity in the room, in view of realization of comfortable air quality in the room. There has been a need for electric motors which are capable of controlling the amount of air blowing depending on the humidity change and, further, are capable of facilitating adjustments of specifications, such as air-quantity/static-pressure characteristics and a plurality of air-quantity settings, without necessitating increased circuit spaces, in particular, and without using specific sensors or microcomputers.